1. Field of the Invention
The present invention is generally directed toward manufacturing methods and, more particularly, toward a method and device for setting a tappet screw.
2. Description of Related Art
Tappet clearance is the distance between a bottom surface of an adjustment or tappet screw and an upper surface of a valve. Different methods and devices for setting tappet clearance are known in the art. One such automatic method for setting tappet clearance involves a method of sensing valve movement and controlling a tappet screw setting in response to sensed valve position.
Methods and devices for manually adjusting tappet screws are also known in the art. When using such devices, it is a common practice for an assembler to walk along and manually adjust the tappet clearance as the engine travels on the assembly line. In accordance with one conventional method, the crankshaft/cam is put in the proper angular orientation, and feeler gauges are inserted between the camshaft and the rocker arm. Thereafter, the tappet screw is rotated or adjusted toward the valve to open the valve. This rotation of the tappet screw continues until the valve spring exhibits a biasing force of a predetermined value against the tappet screw. Accordingly, this method requires a device to turn the tappet screw, and such device must react to the biasing force or load such that further rotation of the tappet screw is prevented upon development of the predetermined valve spring force.
With reference to FIG. 13, a device 100 used in the aforementioned conventional method is shown to include an inner shaft 102, an outer sleeve 104, a bearing block 106, and a dome-shaped handle 108. The outer sleeve 104 includes, at a distal end 110, a nut-receiving socket 112 and, at a proximal end 114, a T-bar type handle 116 that extends radially in opposite directions.
The inner shaft 102 extends through outer sleeve 104 such that a distal end 118 of the inner shaft 102 has a common-type screwdriver head 120 disposed at an open base of the nut-receiving socket 112. The opposite or proximal end 122 of the inner shaft 102 projects outwardly from the proximal end 114 of the outer sleeve 104. Near the proximal end 122, the inner shaft 102 includes a first radially enlarged area to which the proximal end 114 of the outer sleeve 104 is secured, and a second radially enlarged area 126 to which a handle base 128 is secured.
A detent plate 130 is secured adjacent the second radially enlarged area 126 and the inner shaft proximal end 122. The detent plate is affixed to the inner shaft 102 and is essentially captured between the handle base 128 and the bearing block 106. The detent plate 130 includes a series of detents or recesses 132, which are adapted to receive spring-biased balls 134 that are secured in the bearing block 106. The proximal end 122 of the inner shaft 102 defines a longitudinally-extending mounting portion that the bearing block 106 is secured over.
The bearing block 106 provides a center passage that accommodates first and second bearings 137. The bearings 137 rotatably receive the mounting portion of the inner shaft proximal end 122. The dome-shaped handle 108 is affixed over the bearing block 106 for grasping and rotation thereof by the user. The balls 134 are secured in a face or surface at a first end of the bearing block 106.
The balls 134 are biased by springs 136 in a direction away from the bearing block 106 and toward the distal ends of the outer and inner shafts. The balls 134 are received in the detents 132 provided by the detent plate 130. The engagement between the balls 134 and the detent plate 130 serves as the driving connection between the bearing block/handle and the inner shaft 102. The level of spring bias is adjustable by, for example, adjustment screws 138.
Accordingly, with the device illustrated in FIG. 13, and with reference to the valve actuation system illustrated in FIG. 1, rotation of the tappet screw is accomplished by rotating the handle 108. The tappet screw engages the valve and forces the valve stem toward the engine cylinder against the bias of the valve spring. When the force of the valve spring reaches a predetermined desired level (i.e., the load on the inner shaft), the biasing force of the spring-loaded balls is overcome, and the balls 134 slip from the detents 132, giving the worker tactile and aural feedback that the desired pre-load has been accomplished.
Unfortunately, rotation of the handle 108 past the point wherein the balls 134 initially slip from the detents 132, causes the balls 134 to quickly and repeatedly seat into the detents and unseat from the detents. The repeated engagement/disengagement of the balls with the detents is believed to cause the screwdriver to be further rotated or driven, and thus over-driven. This belief is based upon the fact that use of the device illustrated in FIG. 13 has created inconsistent and non-repeatable results.
Therefore, there exists a need in the art for a device to overcome or minimize the deficiencies in the art and properly set the tappet screw. Accordingly, there exists a need in the art for a device for manually setting tappet clearance that will have repeatable, consistent results. There also exists a need in the art for a method for manually setting tappet clearance or preload.
The present invention is directed toward removing or minimizing the above-noted problems in the art and toward providing an improved method and device for setting tappet screw clearance. The present invention is further directed toward an improved method and device for manually setting tappet clearance or preload that will have repeatable, consistent results.
In accordance with the present invention, a tappet screw adjusting device includes an outer sleeve, an inner shaft, a bearing block, a handle, and a load-responsive assembly between the bearing block and the inner shaft. The load-responsive assembly is designed such that, when the load on the inner shaft is below a predetermined level the bearing block and the said inner shaft are coupled for common rotation. Alternatively, when the load on the inner shaft is above the predetermined level, the bearing block is rotated while the inner shaft remains stationary.
In further accordance with the present invention, the load-responsive assembly includes a friction plate and a tension setting device. The tension setting device is coupled to the bearing block while the friction plate is in frictional contact with a member that rotates with the inner shaft.
In further accordance with the present invention, the friction plate serves as a frictional coupling between the inner shaft and the tension setting device. The tension setting device is threadably secured to the bearing block, and the friction plate includes a projection that is received in a groove in the tension setting device. Therefore, rotary motion of the tension adjusting device is translated into axial movement of the friction plate.